Methods of forming openings and methods of controlling the degree of taper of openings

ABSTRACT

Methods of forming contact openings and methods of controlling the degree of taper of contact openings are described. In one implementation, a layer is first etched through a contact mask opening using a first set of etching conditions. The etching conditions provide a first degree of sidewall taper from vertical, if etching completely through the layer. After the first etching, the layer is second etched through the contact mask opening using a second set of etching conditions. The second set of etching conditions provide a second degree of sidewall taper from vertical, if etching completely through the layer. The second degree of sidewall taper is different from the first degree of taper. In another embodiment, a material through which a contact opening is to be etched to a selected depth is formed over a substrate. A masking layer having an opening therein is formed over the material. The material is first etched through the opening with the first etch having a first selectivity relative to the masking layer. After the first etch, and at a depth which is less than about 50% of the selected depth, the material is second etched, with the second etch having a second selectivity relative. to the masking layer which is greater than the first selectivity. In a preferred implementation, the second degree of selectivity is achieved by modifying an etch parameter during the etching of the contact opening.

RELATED PATENT DATA

This patent is a continuation application of U.S. patent applicationSer. No. 09/031,090 which was filed on Feb. 26, 1998 now U.S. Pat. No.6,074,957

TECHNICAL FIELD

This invention relates to methods of forming contact openings and tomethods of controlling the degree of taper of contact openings.

BACKGROUND OF THE INVENTION

When integrated circuitry is formed, contact openings are often formedthrough insulative material for establishing electrical communicationwith the integrated circuitry. Such contact openings are typicallysubsequently filled with conductive material, such as a metal orpolysilicon, whereby electrical communication is established with theintegrated circuitry.

Contact openings are often formed to be fairly narrow; and, it isdesirable from a design standpoint to form the contact openings to havesidewalls which are as near vertical as possible. This helps to ensurethat the contact area at the bottom of the contact opening issufficiently large to desirably cover and/or expose conductive materialwith which electrical communication is desired. As aspect ratios, i.e.the height-to-width ratio, of contact openings increase, it becomesincreasingly important to ensure that the dimension of the bottom of thecontact opening is sufficiently large to provide adequate coverage forconductive material which is subsequently formed therein. For narrowcontact openings, such is accomplished by maintaining the sidewalls ofthe contact opening as near vertical as possible.

Referring to FIGS. 1 and 2, two exemplary contact opening etch profilesare indicated generally at 100, 100 a respectively. FIG. 1 shows asubstrate 102 with a layer of insulative material 104 formed thereover.A masking layer 106 such as photoresist is formed over insulativematerial 104 and is subsequently patterned to define a contact openingpattern. Contact opening 108 is etched using an etch which is highlyselective relative to masking layer 106. Hence, while a desirably highlevel of selectivity ensures that masking layer 106 remains over thesubstrate, the subsequent etch profile is unsatisfactorily tapered. FIG.2 shows a substrate 100 a in which like numbers from FIG. 1 have beenutilized with the suffix “a”. There, a contact opening 108 a is etchedthrough layer 104 a using an etch with a comparatively lower degree ofselectivity relative to an overlying masking layer (not shown). Thelower degree of selectivity results in a contact opening profile with amore desirable degree of taper. Yet, the overlying masking layer can becompletely removed, thereby undesirably opening up other substratefeatures to etching.

This invention arose out of concerns associated with providing methodsof forming contact openings having sidewalls which are generallyvertical within desired tolerances. This invention also arose out ofconcerns associated with providing methods for controlling the degree oftaper of contact openings.

SUMMARY OF THE INVENTION

Methods of forming contact openings and methods of controlling thedegree of taper of contact openings are described. In oneimplementation, a layer is first etched through a contact mask openingusing a first set of etching conditions. The etching conditions providea first degree of sidewall taper from vertical, if etching completelythrough the layer. After the first etching, the layer is second etchedthrough the contact mask opening using a second set of etchingconditions. The second set of etching conditions provide a second degreeof sidewall taper from vertical, if etching completely through thelayer. The second degree of sidewall taper is different from the firstdegree of taper. In another embodiment, a material through which acontact opening is to be etched to a selected depth is formed over asubstrate. A masking layer having an opening therein is formed over thematerial. The material is first etched through the opening with thefirst etch having a first selectivity relative to the masking layer.After the first etch, and at a depth which is less than about 50% of theselected depth, the material is second etched, with the second etchhaving a second selectivity relative to the masking layer which isgreater than the first selectivity. In a preferred implementation, thesecond degree of selectivity is achieved by modifying an etch parameterduring the etching of the contact opening.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred embodiments of the invention are described below withreference to the following accompanying drawings.

FIG. 1 is a diagrammatic side sectional view of a semiconductor waferfragment having a contact opening thereover which has been etchedutilizing an etch which is highly selective relative to an overlyingmasking layer.

FIG. 2 is a view which is similar to the FIG. 1 view, only one whichshows a contact opening which has been etched using an etch with a lowdegree of selectivity relative to a previously-formed masking layer.

FIG. 3 is a diagrammatic side sectional view of a semiconductor waferfragment in process in accordance with one aspect of the invention.

FIG. 4 is a view of the FIG. 3 wafer fragment at a different processingstep.

FIG. 5 is a view of the FIG. 3 wafer fragment at a different processingstep.

FIG. 6 is a view of a portion of a sidewall of a contact opening whichis etched in accordance with one aspect of the invention.

FIG. 7 is a graph which depicts taper angle versus step 1 etch depth.

FIG. 8 is a graph which depicts contact area versus step 1 etch depth.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

This disclosure of the invention is submitted in furtherance of theconstitutional purposes of the U.S. Patent Laws “to promote the progressof science and useful arts” (Article 1, Section 8).

Referring to FIG. 3, a semiconductor wafer fragment in process is showngenerally at 10 and comprises a semiconductive substrate 12. In thecontext of this document, the term “semiconductive substrate” is definedto mean any construction comprising semiconductive material, including,but not limited to, bulk semiconductive materials such as asemiconductive wafer (either alone or in assemblies comprising othermaterials thereon), and semiconductive material layers (either alone orin assemblies comprising other materials). The term “substrate” refersto any supporting structure, including, but not limited to, thesemiconductive substrates described above.

In this example, substrate 12 has a diffusion region 13 formed thereinwith which electrical communication is desired. A layer 14 of materialis formed over substrate 12 and through which a contact opening having aselected depth is to be etched. An exemplary material for layer 14 is anoxide material such as borophosphosilicate glass (BPSG) formed to anexample thickness of 2.2 micron. In a preferred embodiment, layer 14comprises a single layer of BPSG. Other materials and numbers of layerscan, of course, be used. A masking layer 16 is formed over layer 14 andsubsequently patterned to define a contact mask opening 18 which exposesa surface portion 20 of layer 14. An exemplary material for maskinglayer 16 is photoresist.

Referring to FIG. 4, material of layer 14 is first etched throughcontact mask opening 18 using a first set of etching conditions orparameters which collectively provide a first degree of sidewall taperfrom vertical were etching to occur completely through the layer.

Referring to FIG. 5, and at an intermediate point proximate a first etchdepth, layer 14 is second etched using a second set of etchingconditions or parameters which provide a second degree of sidewall taperfrom vertical were etching to occur completely through the layer. Thesecond etching continues to proximate the depth selected for contactopening 22. In the illustrated example, the selected depth is one whichis sufficient to reach diffusion region 13. The second etching can,however, be terminated before reaching the ultimate depth to which thecontact opening is to be etched. Preferably, the second degree ofsidewall taper is different from the first degree of sidewall taper.Even more preferably, the first degree of sidewall taper is less is thanthe second degree of sidewall taper.

Alternately considered, the first set of etching conditions are selectedto provide a first degree of selectivity relative to masking layer 16.At an etch depth which is less than about 50% of the selected depth ofthe desired contact opening, the etching conditions or parameters arechanged to provide the second etch with a second selectivity relative tomasking layer 16 which is greater than the first selectivity. In theillustrated and preferred embodiment, the first and second etches oflayer 14 are dry etches.

Referring to FIG. 6, a portion of a sidewall of contact opening 22 isindicated at 24. Such is displaced from a vertical line 25, or has adegree of taper from top-to-bottom away from vertical which defines anangle θ, wherein θ is preferably no greater than about 3°. Even morepreferably, θ is around 1.5°.

Referring to FIGS. 7 and 8, two graphs are set forth which describe datameasured in a reduction to practice example. In such example, a LAM TCP9100 high density oxide etcher was utilized to form contact openings asdescribed above. BPSG was utilized as the layer through which thecontact opening was etched, and the selected desired depth of thecontact opening was around 2 microns. In conducting the first etch ofthe BPSG, the following etch conditions or parameters were utilized:1050 Watts Source/1050 Watts Bias; 10 sccm C₂HF₅, 15 sccm CHF₃, 5 sccmCH₂F₂, at 15 mTorr. The first set of etch conditions comprise a firstratio of carbon to fluorine sufficient to provide a first degree ofselectivity relative to the masking layer, e.g. the photoresist. Thesecond etch was conducted with the following etch conditions orparameters: 700 Watts Source/700 Watts Bias; 20 sccm C₂HF₅, 10 sccmCHF₃, 10 sccm CH₂F₂ at 20 mTorr. The second set of etch conditionscomprise a second ratio of carbon to fluorine to provide a second degreeof selectivity relative to the masking layer which is different, andpreferably greater than the first degree of selectivity. Preferably, thesecond ratio is lower than the first ratio.

Table 1 below describes data associated with the first and secondetches. The first and second columns designated as “T1” and “T2”respectively, are the respective times, in seconds, of the first andsecond etches. The “Depth” column describes the depth, in microns, ofthe ultimately-etched contact opening, e.g. the selected depth. The “S1Depth” column describes the depth, in microns, at which the first etchwas modified to the second etch. The “Taper Angle” column describes theangle of taper of the sidewalls of the ultimately-etched contact openingaway from vertical.

Referring to FIG. 7, contact opening taper angle is plotted in degreesaway from vertical, as a function of the depth at which the first etchwas changed to the second etch. A plurality of data points are shown atA, B, C, D, E, F, and G. Each data point corresponds to an individualrow in Table 1. For example, data point G (last row in Table 1)describes a contact opening having a taper angle slightly larger than1.5°. Such contact opening was formed, referring to Table 1, byconducting the first etch for 30 seconds, modifying the etch chemistryor parameters, and then conducting the second etch for 150 seconds. Suchresulted in an intermediate switch point between etches of around 0.44micron, for a resulting contact opening depth of around 2.6 micron.

TABLE 1 Taper T1 T2 Depth S1 Depth Angle (A) 1 150 2.3 0.015 3.005 (B) 5145 2.2 0.073 2.434 (C) 10 140 2.3 0.147 2.434 (D) 15 135 2.3 0.2202.148 (E) 20 130 2.3 0.293 2.005 (F) 40 110 2.2 0.587 2.148 (G) 30 1502.6 0.440 1.575

Referring to FIG. 8, contact area at the bottom of the contact openingis plotted as a function of the depth at which the first etch waschanged to the second etch for the same data points. Utilizing the sameparameters or etch conditions as described above in connection with FIG.7, the largest contact area observed appeared where the degree of taperaway from vertical was the smallest, i.e. data point G Such isdesirable, as mentioned above, from the standpoint of opening up as muchpotential conductive contact area within desired tolerances

Accordingly, methods of the present invention enable a degree of contactopening taper to be controlled and selected. Such methods also providefor contact openings having generally vertical sidewalls which. increasethe contact area at the bottom of the contact opening.

In compliance with the statute, the invention has been described inlanguage more or less specific as to structural and methodical features.It is to be understood, however, that the invention is not limited tothe specific features shown and described, since the means hereindisclosed comprise preferred forms of putting the invention into effect.The invention is, therefore, claimed in any of its forms ormodifications within the proper scope of the appended claimsappropriately interpreted in accordance with the doctrine ofequivalents.

What is claimed is:
 1. A method of controlling the degree of taper of anopening formed in a material, comprising: forming a layer of materialinto which an opening having a first depth is to be etched; forming amasking layer over the layer of material; exposing a portion of thelayer of material through the masking layer; conducting a first dry etchof the exposed portion of the layer of material utilizing a first etchchemistry having a first degree of selectivity relative to the maskinglayer, the first etch chemistry comprising a first ratio of carbon tofluorine to provide a first degree of selectivity relative to themasking layer; at a second depth which is about 50% or less of the firstdepth, modifying the first etch chemistry to provide a second dry etchchemistry, the second dry etch chemistry comprising a second ratio ofcarbon to fluorine to provide a second degree of selectivity relative tothe masking layer, the second ratio being lower than the first ratio andthe second degree of selectivity being greater than the first degree ofselectivity; conducting a second dry etch of the layer of material downto the first depth using the second etch chemistry; and the openinghaving a sidewall and a degree of taper along a majority of the sidewallwhich is no greater than about 3-degrees away from vertical; the firstetch chemistry generating a first degree of the taper of the sidewallfrom vertical and the second dry etch chemistry generating a seconddegree of the taper of the sidewall from vertical; the first degree ofthe taper of the sidewall being less than the second degree of the taperof the sidewall.
 2. The method of claim 1, wherein the first depth isless than or equal to about 2 microns.
 3. The method of claim 1,wherein: the first depth is less than or equal to about 2 microns; andthe second depth at which the first etch chemistry is modified is about0.4 micron.
 4. The method of claim 1, wherein the layer of materialcomprises an oxide material.
 5. The method of claim 1, wherein the layerof material comprises borophosphosilicate glass.
 6. The method of claim1, wherein the masking layer comprises photoresist.
 7. The method ofclaim 1, wherein: the layer of material comprises borophosphosilicateglass; and the masking layer comprises photoresist.
 8. The method ofclaim 1, wherein: the layer of material through which the contactopening is to be formed comprises an oxide material; and the conductingof the first and second dry etches comprises conducting said etches witha high density oxide etcher.
 9. A method of forming an openingcomprising: providing a substrate within an oxide etcher, the substratehaving an oxide layer through which an opening is to be etched; forminga layer of photoresist over the oxide layer; patterning the photoresistto define a mask opening; first etching into the oxide layer through themask opening using a first set of etching conditions, the first set ofetching conditions comprising a first ratio of carbon to fluorine toprovide a first degree of selectivity relative to the photoresist; afterthe first etching, second etching into the oxide layer through the maskopening using a second set of etching conditions, the second set ofetching conditions comprising a second ratio of carbon to fluorine toprovide a second degree of selectivity relative to the photoresist, thesecond ratio being lower than the first ratio and the second degree ofselectivity being greater than the first degree of selectivity; and thefirst etching and second etchings forming an opening extending into theoxide, the opening having a sidewall; the first etching generating afirst degree of taper of the sidewall from vertical and the secondetching generating a second degree of taper of the sidewall fromvertical; the first degree of taper of the sidewall being less than thesecond degree of taper of the sidewall.
 10. A method of forming anopening in a layer of oxide material comprising: providing a layer of anoxide material over a substrate; first etching into the oxide materialthrough a mask opening in a photoresist material using a first set ofetching conditions which are defined by a first degree of sidewall taperfrom vertical, the first etching forming an opening in the oxidematerial; after the first etching, second etching into the oxidematerial through the mask opening using a second set of etchingconditions which are defined by a second degree of sidewall taper fromvertical, the second degree of sidewall taper being different from thefirst degree of taper; the second etching extending the openingdownwardly into the oxide material; the first degree of sidewall taperis less than the second degree of sidewall taper; and the first andsecond etchings have different degrees of selectivity relative to thephotoresist material.
 11. A method of forming an opening through a layerof borophosphosilicate glass (BPSG), comprising: providing a layer ofBPSG over a semiconductive material substrate; first etching into theBPSG through a mask opening using a first set of etching conditionswhich are defined by a first degree of sidewall taper from vertical, thefirst etching forming an opening in the BPSG; after the first etching,second etching into the BPSG through the mask opening using a second setof etching conditions which are defined by a second degree of sidewalltaper from vertical, the second degree of sidewall taper being differentfrom the first degree of taper; the second etching extending the openingdownwardly into the BPSG; and wherein the first degree of sidewall taperis less than the second degree of sidewall taper.